Note that -- as I pen these words -- for a $12 pledge there's still an "Open-Source Special, DIY/Tinkerer's Kit" that includes two custom-fabricated, specially-silvered NeoLucida prisms so you can make your own camera lucida design!

I think I heard about that app -- but doesn't it just use the iPad's camera to present a faint image in the iPad's screen that you then trace around? I suppose you coudl then print this off and fill in the details. Have you used the app? Can you tell us about it?

One could connect a digital camera (or a computer with a digital photograph) to a PC projector. Projecting the image onto a piece of paper or a large screen would allow unlimited time for tracing and leisurely detailing of the image.

I use the Camera Lucida app. With my iPad. It works better than the traditional camera lucida, Art-o-graph, or any other optical image transfer tool that I have encountered. I, too, pledged on the Kickstarter campaign, and will receive mine in the first batch – I mainly did it out of curiosity, and add to my collection of traditional Camera Lucida's.
Link for Camera Lucida iOS:
https://itunes.apple.com/us/app/camera-lucida/id362499096?mt=8